.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
.\"
.\" %%%LICENSE_START(VERBATIM)
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.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\"
.\" Permission is granted to copy and distribute modified versions of this
.\" manual under the conditions for verbatim copying, provided that the
.\" entire resulting derived work is distributed under the terms of a
.\" permission notice identical to this one.
.\"
.\" Since the Linux kernel and libraries are constantly changing, this
.\" manual page may be incorrect or out-of-date.  The author(s) assume no
.\" responsibility for errors or omissions, or for damages resulting from
.\" the use of the information contained herein.  The author(s) may not
.\" have taken the same level of care in the production of this manual,
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.\" %%%LICENSE_END
.\"
.\" References consulted:
.\"     Linux libc source code
.\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
.\"     386BSD man pages
.\" Modified Sat Jul 24 17:56:43 1993 by Rik Faith (faith@cs.unc.edu)
.\" Added history, aeb, 980113.
.\" 2005-05-05 mtk: added strcasestr()
.\"
.TH STRSTR 3  2021-08-27 "GNU" "Linux Programmer's Manual"
.SH NAME
strstr, strcasestr \- locate a substring
.SH SYNOPSIS
.nf
.B #include <string.h>
.PP
.BI "char *strstr(const char *" haystack ", const char *" needle );
.PP
.BR "#define _GNU_SOURCE" "         /* See feature_test_macros(7) */"
.B #include <string.h>
.PP
.BI "char *strcasestr(const char *" haystack ", const char *" needle );
.fi
.SH DESCRIPTION
The
.BR strstr ()
function finds the first occurrence of the substring
.I needle
in the string
.IR haystack .
The terminating null bytes (\(aq\e0\(aq) are not compared.
.PP
The
.BR strcasestr ()
function is like
.BR strstr (),
but ignores the case of both arguments.
.SH RETURN VALUE
These functions return a pointer to the beginning of the
located substring, or NULL if the substring is not found.
.PP
If
.I needle
is the empty string,
the return value is always
.I haystack
itself.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.ad l
.nh
.TS
allbox;
lbx lb lb
l l l.
Interface	Attribute	Value
T{
.BR strstr ()
T}	Thread safety	MT-Safe
T{
.BR strcasestr ()
T}	Thread safety	MT-Safe locale
.TE
.hy
.ad
.sp 1
.SH CONFORMING TO
.BR strstr ():
POSIX.1-2001, POSIX.1-2008, C89, C99.
.PP
The
.BR strcasestr ()
function is a nonstandard extension.
.SH SEE ALSO
.BR index (3),
.BR memchr (3),
.BR memmem (3),
.BR rindex (3),
.BR strcasecmp (3),
.BR strchr (3),
.BR string (3),
.BR strpbrk (3),
.BR strsep (3),
.BR strspn (3),
.BR strtok (3),
.BR wcsstr (3)
.SH COLOPHON
This page is part of release 5.13 of the Linux
.I man-pages
project.
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at
\%https://www.kernel.org/doc/man\-pages/.
